Aqueous bleaching agent suspensions containing peroxycarboxylic acids are known from British Patent No. 1,535,804, corresponding to U.S. Pat. Nos. 3,996,1522 and 4,017,412. Such bleaching agent compounds can be added with advantage to alkaline washing mixtures in washing machines or be used themselves as bleaching agents.
The use of bleaching agent suspensions, in comparison to solid, generally particulate bleaching agent compounds, has the advantage of being able to eliminate expensive and, in the case of peroxycarboxylic acids, drying and granulating steps which have reliability problems. However, in addition to being effective in use, bleaching agent suspensions must satisfy certain essential conditions which are needed for smooth and reliable handling in the commercial and domestic areas. These conditions include, good chemical stability and especially physical stability as regards a solid liquid phase separation and handling safety, even in the event of leakage or spaying of the suspension from barrels.
The aqueous bleaching agent compounds according to British patent No. 1,535,804 contain essentially water-insoluble peroxycarboxylic acids which are suspended in an aqueous carrier liquid containing a thickening agent. These compounds are thickened until gelled and their viscosity is 200 to 100,000 centipoises. Starches, cellulose derivatives, natural rubbers, synthetic organic polymers as well as inorganic thickening agents of the group of colloidal silicic acids and hydrophilic clays are mentioned as thickening agents.
A major disadvantage of the bleaching agent compounds of British Patent Patent No. 1,535,804 is that they usually have insufficient storage resistance, at least to the extent that they are not gelled systems. The suspensions are physically unstable, since the solid phase separates from the liquid phase. This instability usually becomes noticeable directly after preparation of the suspension, frequently within one day or even hours. On the other hand, experts in this field call for greater storage resistance, preferably one of several weeks.
Another disadvantage caused by the physical instability with phase separation concerns the redispersibility of the thickened phase containing the peroxycarboxylic acid, which is unacceptably difficult. Finally, bleaching agent suspensions prepared with organic thickening agents present an increased potential for danger because, after a suspension has been spilled, and especially after the spilled material has dried, substantially non-desensitized peroxycarboxylic acid remains. Attempts to reduce the potential for danger by adding a desensitizing agent such as sodium sulfate were not successful because the properties of the suspensions deteriorated even more, cf published European Patent Application No. 0,176,124, page 2, paragraph. 1 and European Patent Application No. 0,160,342, page 3, paragraph 3. There has been no lack of attempts to create bleaching agent suspensions with improved storage resistance and a lesser potential for danger. Thus, European Patent Application No. 0, 160,342 teaches aqueous bleaching agent suspensions in which water-insoluble peroxy acids are suspended in an aqueous liquid containing a surfactant and an electrolyte. These pourable suspensions preferably contain sodium sulfate as well as an anionic and/or nonionic surfactant. A considerable disadvantage of these systems, namely, the very limited chemical stability, was eliminated by the use of alkali metal salts of alkyl benzene sulfonic acids, cf. European Patent Application No. 0,176,124 or by adjusting the pH to the range 3.5 to 4.1, cf. EP-A- 0,201,958. However, the physical stability of these surfactant-structured bleaching agent suspensions does not satisfy the requirements for such systems, as is shown in reference examples.
Thus, the need for a bleaching agent suspension which is sufficiently stable from a chemical and a physical standpoint has not been satisfied by the previously known thickening agent systems or surfactant-structured systems.